SR TESOENOS” 
er 
a 
. 
= 
sailed ee acute, when the angle is from 10° to 30°, 
as in calcareous fpar ; very acute, from 30° to 50”, as in 
to 70°, as In calcareous {par ; 
reCtangular, as 
F in honey- 
> 
s in sie s {par ; 
ane, 
r e former are em common ; the la tter 
are aittingoithed according to the pofition of the a 
which is either concave, as in fluor {par ; co di 
rie par ; and conical, as ing 
¢. The F eat of the Cryftal. ~Cryfials a are either full and 
perfe&, which is moft a hollowed at 
the ee as in gre 
the three-fided pyramidal pain ous ae 
Modifications of the fundamental ch anges 
or alterations whic rsa on the fanda mental form are 
three ; truncati ion, bevelmen Molle “ mi 
ion, viz. its edges, and angles; and the determi- 
nation the trancation, which ates to ie fituation as it 
occurs at th angles ; its nitude ; its ced 
jacent 
er an even or a curv ah 
evelment—takes place an = di Sa terminal planes, 
les, are re placed e o {m 
ach by aller converging 
planes anne ie Tn this we have to confider 
the parts a e determination of the bevelment —The parts 
are the a the angles, and the 
er there are two kinds, viz the proper 
planes :—the det 
be confidered its fituation, as it ta 
the bevelment, which is either uninterrupted or interrupted, 
and this latter either once interrupted, as in the double three- 
or twice interrupted, as 
evelment, 
_ 
eee tion. ries he fundamental figure is faid to be 
nated when its angles or terminal a are replaced 
oO 
€ 
fize, form, and application; to c age of the fummit of 
the acumination, which is either iit and rectangular, or 
acute ; to the magnitude of the — has laftly, to 
its termination, which is either a point 
e. Multiplied Modifications of the yin nd Figure.— 
Befides the fimple alterations or modifications -: the funda- 
mental fizure, we of-en meet with mu inane or complicated 
alterations. Thefe are faid to be co- —_ n feveral 
ai kinds of ie ration occur togeth an. ‘a8 aaa 
and bevelments ; ae fupe is aati when feveral of the = 
kind are placed o a ee s; for a nce, when one 
cumination is (ieee ted by. one or m In de feribing 
thefe alterations, oo ought to be Gencoaed firft which 
are the largeft and moft effential. 
é peas and Aggregation i ie Cryftals.—Ac- 
cording to this, cryfta als are either fin or aggregated. 
i ed, or fuper- 
ter, however, are very 
Ya 
rey antiziony :—man ou ee aay are dif- 
tributed according to the a nthey affume, whence the follow- 
y VIZ. feopiform or fafcicular ; : 
whes aggregated, acicalar me pillary cr 
a common ¢ 
3 
@ 
sect 
Lad 
8 
7 
elongated, equally 
thick ae le nenipe together, are of this defcrip- 
ion, as in columnar barytes :—pyramidal ; many cryftals 
parallel : one ee but of which thofe in the middle 
are the higheft, and the others decline on all fides, thus 
together, as to refemble 
with the variety of calcareous fpar, called rofe fpar, from 
Joachimithal :—amygdaloid; formed by tables accumulated 
in fuch a manner as to have an Seca form, as in ba- 
rytes :—globular ; as in iron pyrites re- 
gation in which the axes of all the eryftals lie in one di- 
rection, like a tring of pearls, as it is feen in calcareous 
{par, vitreous filve 
be Magnitude of Cryftals, with regard to which they 
are divided ints feven varieties, viz. uncomm.nly large ; two 
feet and upw ards i in length, as in in rock cryftal :—very large ; 
asin beryl, calcareors {par: 
—large ; from fix inches to two in length: :—middle-fized ; 
from two inches to half an inch :—fmall; from half an inch 
to 3th of an inch :—very fmall; from kth of an inch in 
length, to fuch as dae juft be diftinguifhed by the naked hae 
as in hornfilv microfcopic ; whofe form cannot be diftin 
guifhed by the el eye, as in native gold, 
According to the relative dimenfions, when bompered with 
others, a faet are diftinguifhed into fhort and low, long 
and high, br and narrow, thick and thin, needle like, 
ss ipicelan and globular, or teffular 
4. LExtrancous external Forms, or Petrifaiions, which are 
divided i fea tho fe of animals and thofe of vegetables. See 
7 c 
ON 
el Surface.—This is the fecond particular 
ee charadter of folid minerals ; the following are its va- 
rieties, ofz. uneven ; having sh asad elevations and de- 
preffions, as in aca om ar; when the elevations 
are 
